Brake anti-skid system

ABSTRACT

An electromagnetic sensing device on the wheels of a vehicle produces a voltage that is used to keep a relay switch in a central power circuit open. Upon loss of this voltage due to stoppage of a wheel during skidding, the power circuit closes a solenoid valve in the hydraulic brake line, preventing the brake fluid pressure from dropping, and thus keeping the brake disc from rotating. Simultaneously, a square wave generator in the power circuit produces a square wave voltage to activate a solenoid coil operating a piston for automatically cycling the pressure in the brake line, maintaining the brake torque at or near the point of critical slip.

United States Patent 1 1 Mikaila [4 1 May S, 1973 541 BRAKE ANTI-SKIDSYSTEM 3,361,487 1/1968 Vriend 303 65 75 Inventor: Joseph J. Mikaila,Southfield, Mich. 2 :22:32; :233: '5 3g [73] Assignee; The United Statesof America as 3,558,197 1/1971 Lueck et al ..303/21 BE represented bythe Secretary of the Army, Washington, Dc Primary Exammer-Duane A. RegerAttorney-Edward Kelly, Harry M. Saragovitz, Her- Filed: 19, 1971 bertBerl and John F. Schmidt [2]] Appl. No.: 125,985

[57] ABSTRACT Related Apphcation Dam An electromagnetic sensing deviceon the wheels of a [63] Continuation-impart of Ser. No. 873,428, Nov. 3,which: Produces g that is used to p a relay 19 9 abandonc switch in acentral power circuit open. Upon loss of this voltage due to stoppage ofa wheel during 52 us. Cl. ..303/21 F, 303/61 skidding, the Power CircuitCloses a solfimid valve in 51 Int. Cl. ..B60t 8/12 the hydraulic brakeline, Preventing the brake fluid 58 Field or Search ..303/21 F, 21 BE, Pfmm dropping, and "111s keeping the brake 303/6l63,68-69,6,10; 188/181disc from rotating. Simultaneously, a square wave generator in the powercircuit produces a square wave [56] References Cited voltage to activatea solenoid coil operating a piston for automatically cycling thepressure in the brake UNITED STATES PATENTS line, maintaining the braketorque at or near the point of critical slip. 2,959,012 11/1960 Johnson....303/61 X 3,089,734 5/1963 'Jankus ..303/61 X 14 Claims, 4 DrawingFigures PATENTEDHAY elm V $731,979

SHEET 1 0F 3 INVENTOR ATTORNEYS PATENTEU W 81975 SHEET 2 OF 3 FIG-3 Z5INVENTOR,

JOSEPH J. MIKAILA Harry M. Sarc'1govlfZ,Edrvard-l Kell 34 Herberf Ber/ 8John F. Scnmidr ATTORNEYS.

BRAKE ANTI-SKID SYSTEM RELATED APPLICATIONS This application is acontinuation-in-part of my application Ser. No. 873,428, filed Nov. 3,1969, now abandoned and relating to a Brake Anti-Skid System.

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without payment to meof any royalty thereon.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to antiskid brake systems and more particularly to an anti-skidbrake system having a minimum response time.

2. Description of the Prior Art Present anti-skid brake systems attemptto keep the vehicle wheels in a braking situation whereby the brakingtorque does not exceed a value corresponding to the point of criticalslip between the wheels and the ground. Critical slip is the point wherethe frictional force between a wheel being braked and the surfaceengaging the wheel is at a maximum thus providing minimum stoppingdistance and maximum braking effectiveness with a minimum of tire wearand optimum control of the vehicle being braked.

The present anti-skid systems attempt to keep the vehicle wheelsoperating as close as possible to the critical slip point, which can berepresented as a horizontal line plotted on a graph, the ordinate ofwhich is time and the abscissa is brake line pressure measured in poundsper square inch. These prior art systems, as exemplified by U. S. Pat.No. 3,235,036 employ a rotational motion sensing device mounted on thevehicle wheel which emits either a mechanical or electrical signalwhenever the wheel stops rotating and starts to skid. This signal isreceived by a control circuit which functions to lower the brake-linepressure until the circuit is signaled by the sensing device that thewheel has resumed turning. At this point in time the control circuitraises the brake line pressure until the wheel again stops turningwhereupon the cycle is repeated until the vehicle is brought to a stop.

One disadvantage of the above mentioned prior art systems is that theyare slow in response time while being high in initial cost andmaintenance. The response time, or the time required for each cycle, isrelatively long because of the numerous operations which have to beperformed during each cycle. This longer response time is particularlytrue in a purely mechanical system while the use of quicker responsetimes attained with all electronic systems have the disadvantage ofgreatly increased initial costs and maintenance.

SUMMARY OF THE INVENTION The invention relates to a vehicle brake systemwherein a rotating wheel sends a signal to a central v power circuit.When the braked wheel locks up and stops sending the signal, the powercircuit is closed to operate a valve in the hydraulic brake circuit,isolating the brake from the master cylinder so that fluid pressure inthe brake cylinder may be pulsed below and above lock-up pressure, thepulsing being accomplished by a pump activated on closure of the centralpower circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofa brake control system representing one form of the invention;

FIG. 2 is a schematic control diagram depicting principal components ofa control system;

FIG. 3 is an enlarged sectional view of one component of the apparatusof FIG. I; and

FIG. 4 is another embodiment of the component shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, anoperator-operable actuator 10, here shown as a brake pedal, is pivotallysupported from a fixed portion of a vehicle pivot 12 and is adapted togenerate a pressure in a fluid pressure pump 13 here shown as aconventional hydraulic ram and usually referred to as a master brakecylinder. Pump 13 comprises a cylinder element 14 and a piston element16 of which element 116 is connected to actuator lift. A normally closedswitch 17 is disposed so as to be held open by pedal or actuator II)when the parts are in the operating position shown in FIG. 1; switch 17is allowed to close when actuator 10 is operated to engage the brake toeffect a stop.

Master cylinder 13 is connected at its delivery port with a brakeconduit 18 in which there is provided a normally-open valve 20. Valve 20is spring-biased open and is held closed by a solenoid 21. Valve 20 is astandard, off-the-shelf item, so details need not be disclosed here. Aswill be understood by those skilled in the art, solenoid 21 is connectedto be energized by the central power circuit. A vehicle wheel is shownat 22, and a pressure sensor 23 parallels valve 20 and is connected withbrake conduit 18 on both sides of valve 20 so as to respond to pressureP, in the portion of brake conduit 118 between master cylinder I3 andvalve 20, and to pressure I in the portion of the brake conduit betweenvalve 20 and the brake cylinder.

Sensor 23 is connected to actuate a normally-closed switch 23 in thecentral power circuit; see FIG. 2. Switch 23' is opened in response to acondition of greater pressure P or, expressed mathematically, acondition in which P P,.

A source 24 of fluid at a fluctuating pressure, hereinafter referred toas a pulse pump, is connected with the brake conduit between valve 20and wheel 22. As is best seen in FIG. 3, a cylindrical chamber 25 isfitted with a piston 26 so that the piston is free to move vertically inresponse to fluid pressure in chamber 25. Resilient means 28 is disposedin the upper portion of cylindrical body 3% between end cap 32 and aspring seat structure 33 connected with piston 26, and biases piston 26downward against the bias of the fluid in chamber 25.

At its lower end cylindrical body 30 is covered by a closure or end cap34 and encloses a solenoid 36 which is an off-the-shelfcoil adapted tobe operated from a DC source of power, such as an automobile battery, as

v will be explained below. Pulse pump 24 is in effect a fail-safe"device in that sticking of piston 26 or breakage of spring 28 merelyrequires that the operator fall back on conventional operation of thebreaking system.

In the sectional view at the left of FIG. 1, a typical vehicle wheel 22is illustrated having a brake disc structure 38 rotatable with the wheeland having surfaces 40 adapted to be engaged by suitable friction padmeans 42. The friction pads are normally carried in juxtaposition to thedisc surfaces 40 and are responsive to hydraulic pressure acting onhydraulic cylinders 44 to move the pads 42 into frictional engagementwith the surfaces 40 to effect braking action.

Wheel 22 is provided with suitable sensing means such as a magneticcollar 48 having radial perforations or slots (not shown) of a typedescribed in U. S. Pat. No. 3,450,444 issued June 17, 1969 to RobertI... Ballard. A magnetic pick-up device indicated at 54 is suitablymounted in fixed relation to the wheel such that movement of the collarrelative to the device 54 will generate a D. C. voltage which is passedto the control center indicated by box 56. A relay switch 58 is locatedin control center 56 and is held open by the voltage generated by themagnetic sensing circuit of the rotating wheel.

OPERATION In operation, when the pistons of hydraulic cylinders 44 applysuitable pressure to disc 38 through pads 42 so that disc 38 and wheel22 stop rotating, the wheel is locked with the result that the voltagegenerated in the magnetic pick-up device 54 drops to zero, closing therelay switch 58. At this stage, differential pressure switch 23. isalready closed because pressure P does not exceed pressure P,. The leads60 and 64 connect solenoid 21 and switch 23' through the central controlbox 56. With switches 17, 23 and 58 closed, solenoid 21 is energized sothat valve is automatically closed, isolating the portion of the brakecircuit between valve 20 and wheel 22 from the master cylinder.

It will of course be understood by those skilled in the art that, in thevast majority of cases, the operator or driver of the vehicle will be ina panic stop" situation; he will be standing on" the brake pedal, as theexpression goes. As soon as a wheel stops turning, valve 20 closes andat that instant, P P However, because of the panic conditions, thepressure in the brake conduit on the pedal side of valve 20 risesasymptotically to a value such that P is many times more than P Theclosing of switch 58 as aforesaid completes the central power circuit,including the operating circuit for a voltage oscillator such as asquare wave generator 62 which is located in control box 56. Generator62 sends its alternating polarity current to solenoid 36, preferably viaa cable comprising two conductors 66 and 67 as will be understood bythose skilled in the art. The details of the square wave voltage are notset forth here because frequency, voltage, and current values will varyaccording to specific vehicle needs and will be determined by well knowndesign methods.

The square wave signal results in periodic voltage changes in solenoid36, causing piston 26 to reciprocate, thereby cycling the pressure P inbrake line 46. Thus, when the piston 26 moves upward, the pressure inline 46 and consequently in cylinders 44 drops, allowing the wheel torotate; conversely, downward movement of the piston produces an increasein pressure and results in lock-up of the wheel if the road surface hasnot changed. Because wheel 22 should have some freedom to rotate, relayswitch 58 should have a built-in reopening time delay.

Pulse pump 24 functions until brake pedal 10 is released an amountsufficient for pressure P to fall below pressure P,, allowingdifferential pressure switch 23' to open the circuit for solenoid 21.More specifically, the elements are illustrated functionally in FIG.

. 2, wherein sensor 23 embodies a bridging or movable contact 70 hingedat 72 and insulated from the sensor housing. When pressure P exceedspressure P contact 70 swings counter-clockwise into engagement withcontact 74 which is grounded through the sensor housing. Thus a circuitis completed for coil 76, which pulls armature 78 downward againstspring 80, opening switch 23. The central control circuit is also openedif wheel 22 starts to turn again so as to open switch 58, and by pedal10 reaching its retracted position to open switch 17.

It will be seen from the foregoing that the pressure P obtaining in thebrake circuit between valve 20 and the wheel at the time valve 20 closesis just above the maximum brake line pressure allowable to keep wheel 22rotating, and that pressure P in the system disclosed herein willfluctuate so as to straddle or bracket that maximum pressure. If theroad surface changes while valve 20 is closed, it is probable that theaforesaid maximum pressure will be different for the different surface.The change in road surface can then be communicated to the system by thesimple expedient of the operator taking his foot off pedal 10, and thenre-applying the brake. The system will then react in response to thechanged road surface.

To understand the function of switch 23' in the electric power circuitshown in FIG. 2, consider the circumstances of braking action whichactivates pulse pump 24, and the vehicle moves from the road surfacethat set up the critical pressure P about which the pulsing pressurevaries i.e., from just above the critical pressure to just below thatpressure onto a totally different surface. In many cases, said totallydifferent surface will be sufficiently different so that the cyclingpressure under pulse pump 24 will not straddle the critical pressure forthe new surface, and the wheels remain locked up. As pointed out above,the operator can set up a new critical pressure in the isolated brakecylinder circuit by taking his foot off the pedal completely, so as tore-open brake switch 17.

Such a maneuver requires that the brake pedal be returned all the way toits off position. Under panic conditions, the operator might not allowthe pedal to return far enough to open switch 17 before again hittingthe brake pedal. However, he will probably have pulled his brake footback far enough to reduce pressure P to the point that P; is greaterthan P When that happens, movable contact 70 engages contact 74,completing a circuit for coil 76, and opening switch 23. Thereafter, areapplication of brake pressure to the wheel brakes sets up a newcritical pressure P, in case the wheels lock up, whereupon the cyclicvariation of pressure in the isolated wheel cylinder circuit againbrackets or straddles the pressure P which caused the wheels to lock upon the new" surface, and anti-skid braking is again in effect.

Whether or not the operator brings his foot back far enough to openswitch 17, pressure 1P will exceed pressure P before switch 17 can beopened, thus assuring that the power circuit is opened and assuring thatthe new critical P is established, whether switch 17 opens or not andfor whatever reason.

In addition to the foregoing, it should be noted that a skilled operatorwill soon learn how much pressure he needs to take off the brake pedalto set up the condition without even trying to open switch l7, and hewill thus bring the vehicle back into controlled braking more quicklythan if he had to rely on switch 17 alone.

DESCRIPTION OF FIG. 4 EMBODIMENT Reference will now be had to theembodiment shown in FIG. 4, which shows a pulse pump having alternativeresilient means as well as fluid motor actuation of the pump piston.More specifically,pulse pump 124 is provided with a chamber 125 in whichis disposed a reciprocable piston 126 on a piston rod 127. Instead of aspring 28 as in the FIG. 3 pulse pump, the pulse pump 124 (FIG. 4) isprovided with an accumulator 128 which may be any conventional devicesuch as that disclosed in Mercier US. Pat. No. Re. 23,437 (Dec. 4,1951), which originally issued to Mercier Sept. 23, 1941 as U.S. Pat.No. 2,256,835.

Accumulator 128 carries a pressure which is exposed to the upper surfaceof piston 129 in cylinder 130, piston 129 being secured on rod 127 alongwith pump piston 126. The space under piston 1129 is vented toatmosphere via a vent 131.

In the FIG. 3 pulse pump, piston 26 serves also as an armature for anelectric motor which is solenoid 36. An alternative actuator is shown inthe pulse pump 124 of FIG. 4, wherein a fluid motor 132 is supplied withfluid by means of a valve 133 having a fluidenergy supply connection 134and delivery connections 135a and l35b communicating with upper andlower chambers respectively of fluid motor 132. A solenoid 136, similarto the solenoid 36 of the FIG. 3 embodiment, is connected in the FIG. 4embodiment to the rod 138 which moves the valve spool of valve 133.

More specifically, the fluid energy supplied to connection 134 may beany one of number of conventional types, such as a vacuum, or airpressure, or hydraulic fluid under pressure. Valve 133 may be aconventional centered valve in which the delivery connections 135a and1351; are vented to atmospheric pressure by a connection 140 whensolenoid 136 is deenergized. Such valve and energy systems areconventional and need not be detailed here.

Fluid motor 132 may be any ofa number of conventional types and it willsuffice for the purposes of this invention to indicate that the pressureresponsive element 142 may be a piston, or a diaphragm, or acoinbination of both as here shown, comprising a pistonlike disc 144having a diaphragm type of seal M6 with the inner surface of theoperating cylinder Md of fluid motor 132.

OPERATION OF FIG. 4 EMBODIMENT With the vehicle in motion withoutbraking, switches 17 and 58 are open because the brake pedal is fullyretracted and the wheels are turning. Switch 23 is closed because P PWhen the operator applies the brakes, pedal 10 moves away fromengagement with switch l7, so that switch 117 closes, but switch 58remains open because the wheels are rotating.

If the coefficient of friction is low enough, wheel 22 locks up,whereupon sensor 54 no longer sends a signal to switch 58, so thatswitch 58 closes. The central power circuit shown in FIG. 2 is nowcomplete and solenoid 21 is energized. Solenoid 211 closes valve 2th toisolate that portion of the hydraulic brake circuit between valve 20 andwheel 22.

Meanwhile, chamber and thus also piston 126 are exposed to the lock-uppressure which obtains at P when valve 20 closes. Piston I26 movesupward until the upward force due to pressure P operating on the lowersurface of piston 1126 is balanced by the downward force due toaccumulator 12d acting on the upper surface of piston 129. The chamberbelow piston 129 and both ends of fluid motor 132 are at atmosphericpressure due to vent 131 (for piston I29) and due to the centeredposition of valve 133 which opens both sides of fluid motor 132 toconnection M0.

When the central power circuit of FIG. 2 closes, square wave generator62 is activated, and it applies a voltage of alternating polarity tosolenoid I36. The resulting reciprocation of rod 13% applies alternatingpressure differentials to the opposite ends of fluid motor 132, whichreciprocates piston 126 up and down. Such movement of piston I26 servesto vary the pressure P between a high just above lock-up pressure and alow just below lock-up pressure to provide the desired non-skid braking.

In other respects, operation of the two systems is similar and will beunderstood from what is set forth above in the discussion of theoperation of the embodiment disclosed in FIGS. I 3.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to persons skilled in the art.

I claim:

1. In an anti-skid vehicular braking system having an operator-operablefluid pressure pump to actuate a brake for a vehicle wheel:

a fluid conduit connecting the pump with the brake;

normally open valve means in the conduit;

electrical valve operating means energizeable to close the valve;

an electric power circuit for the valve operating means;

first switch means in the electric power circuit and having a normallyclosed position;

a switch operating means to hold the switch open in response to rotationof said wheel;

a source of fluid at a fluctuating pressure for supplying fluid to saidconduit at a pressure which varies from just above the pressure in theconduit at lockup to a pressure just below the lock-up pressure, saidsource connected and communicating directly with said conduit andresponsive to fluid pressure in said conduit at all times that the valvemeans is held open by its operating means;

said fluid source having electrical actuating means independent of saidvalve operating means connected to receive power from said powercircuit;

and

other switch means to interrupt said power circuit in response tocessation of operation of said pump.

2. A braking system as in claim 1, said fluid source including electricpower generating means of a type which generate an alternating voltage.

3. A braking system as in claim 2, said fluid source including asolenoid operated pump.

4. A braking system as in claim 3, the solenoidoperated pump having apiston exposed and responsive to pressure in said conduit, and resilientmeans biasing the piston against conduit pressure.

5. A braking system as in claim 4, in which said other switch meansincludes a normally closed switch and an operator-operable actuator inengagement with the first-named pump, the switch of said other switchmeans being responsive to the fully retracted position of theoperator-operable actuator to open its normally closed contacts.

6. A braking system as in claim 5, said other switch means including asecond normally-closed switch, and pressure sensitive means connectedwith the fluid conduit on opposite sides of the normally open valvemeans for opening the second normally closed switch when conduitpressure on the brake side of said valve exceeds conduit pressure on thefirst-named pump side of said valve.

7. A braking system as in claim 1, said fluid source including asolenoid-operated pump.

8. A braking system as in claim 7, the solenoidoperated pump having apiston exposed and responsive to pressure in said conduit, and resilientmeans biasing the piston against conduit pressure.

9. A braking system as in claim 8, in which said other switch meansincludes a normally closed switch and an operator-operable actuator inengagement with the first-named pump, the switch of said other switchmeans being responsive to the fully retracted position of theoperator-operable actuator to open its normallyclosed contacts.

10. A braking system as in claim 9, said other switch means including asecond normally closed switch, and pressure sensitive means connectedwith the fluid conduit on opposite sides of the normally open valvemeans for opening the second normally closed switch when conduitpressure on the brake side of said valve exceeds conduit pressure on thefirst-named pump side of said valve.

11. A braking system as in claim 1, in which said other switch meansincludes a normally closed switch and an operator-operable actuator inengagement with the first-named pump, the switch of said other switchmeans being responsive to the fully retracted position of theoperator-operable actuator to open its normally closed contacts.

12. A braking system as in claim 1 1, said other switch means includinga second normally closed switch, and pressure sensitive means connectedwith the fluid conduit on opposite sides of the normally open valvemeans for opening the second normally closed switch when conduitpressure on the brake side of said valve exceeds conduit pressure on thefirst-named pump side of said valve.

3. A braking system as in claim 1, said other switch means including anormally closed switch, and pressure sensitive means connected with thefluid conduit on opposite sides of the normally open valve means foropening the normally closed switch when conduit pressure on the brakeside of said valve exceeds conduit pressure on the opposite side of saidvalve.

14. A braking system as in claim 13, said fluid source includingelectric power generating means of a type which generate an alternatingvoltage.

1. In an anti-skid vehicular braking system having an operatoroperablefluid pressure pump to actuate a brake for a vehicle wheel: a fluidconduit connecting the pump with the brake; normally open valve means inthe conduit; electrical valve operating means energizeable to close thevalve; an electric power circuit for the valve operating means; firstswitch means in the electric power circuit and having a normally closedposition; a switch operating means to hold the switch open in responseto rotation of said wheel; a source of fluid at a fluctuating pressurefor supplying fluid to said conduit at a pressure which varies from justabove the pressure in the conduit at lock-up to a pressure just belowthe lock-up pressure, said source connected and communicating directlywith said conduit and responsive to fluid pressure in said conduit atall times that the valve means is held open by its operating means; saidfluid source having electrical actuating means independent of said valveoperating means connected to receive power from said power circuit; andother switch means to interrupt said power circuit in response tocessation of operation of said pump.
 2. A braking system as in claim 1,said fluid source including electric power generating means of a typewhich generate an alternating voltage.
 3. A braking system as in claim2, said fluid source including a solenoid operated pump.
 4. A brakingsystem as in claim 3, the solenoid-operated pump having a piston exposedand responsive to pressure in said conduit, and resilient means biasingthe piston against conduit pressure.
 5. A braking system as in claim 4,in which said other switch means includes a normally closed switch andan operator-operable actuator in engagement with the first-named pump,the switch of said other switch means being responsive to the fullyretracted position of the operator-operable actuator to open itsnormally closed contacts.
 6. A braking system as in claim 5, said otherswitch means including a second normally-closed switch, and pressuresensitive means connected with the fluid conduit on opposite sides ofthe normally open valve means for opening the second normally closedswitch when conduit pressure on the brake side of said valve exceedsconduit pressure on the first-named pump side of said valve.
 7. Abraking system as in claim 1, said fluid source including asolenoid-operated pump.
 8. A braking system as in claim 7, thesolenoid-operated pump having a piston exposed and responsive topressure in said conduit, and resilient means biasing the piston againstconduit pressure.
 9. A braking system as in claim 8, in which said otherswitch means includes a normally closed switch and an operator-operableactuator in engagement with the first-named pump, the switch of saidother switch means being responsive to the fully retracted position ofthe operator-operable actuator to open its normally-closed contacts. 10.A braking system as in claim 9, said other switch means including asecond normally closed switch, and pressure sensitive means connectedwith the fluid conduit on opposite sides of the normally open valvemeans for opening the second normally closed switch when conduitpressure on the brake side of said valve exceeds conduit pressure on thefirst-named pump side of said valve.
 11. A braking system as in claim 1,in which said other switch means includes a normally closed switch andan operator-operable actuator in engagement with the first-named pump,the switch of said other switch means being responsive to the fullyretracted position of the operator-operable actuator to open itsnormally closed contacts.
 12. A braking system as in claim 11, saidother switch means including a second normally closed switch, andpressure sensitive means connected with the fluid conduit on oppositesides of the normally open valve means for Opening the second normallyclosed switch when conduit pressure on the brake side of said valveexceeds conduit pressure on the first-named pump side of said valve. 13.A braking system as in claim 1, said other switch means including anormally closed switch, and pressure sensitive means connected with thefluid conduit on opposite sides of the normally open valve means foropening the normally closed switch when conduit pressure on the brakeside of said valve exceeds conduit pressure on the opposite side of saidvalve.
 14. A braking system as in claim 13, said fluid source includingelectric power generating means of a type which generate an alternatingvoltage.